The present invention relates to a therapeutic agent for erectile dysfunction. More particularly, it relates to a therapeutic agent for erectile dysfunction containing as the active ingredient prostaglandin derivatives of general formula (I), nontoxic salts thereof or cyclodextrin clathrate compounds thereof, wherein each symbol is as defined below. 
Male sexual dysfunction, in particular erectile dysfunction, is attributed to various causes such as aging, operation of prostate gland, injury of nerve cord, and diabetes. However, what is common in these causes is that a decrease of blood flow into the corpus cavernosum penis is the direct cause. As one of methods of treating it, administration of a vasodilator such as prostaglandin E1 (hereinafter abbreviated as PGE1) has been considered effective (DICPxe2x80x94The animal of Pharmacotherapy, 5, 363 (1991)). However, PGE1 has problems that it is attended with pain (angialgia) upon administration, that the drug itself is unstable and so forth.
On the other hand, it has been found that prostaglandin E2 (hereinafter, abbreviated as PGE2) that has oxytocic effect also has utility for erectile dysfunction. This has made it unclear whether or not the erectile dysfunction improving action of PGE1 is simply based on its vasodilating action without reservation (WO93/00894).
PGE2 is known to be as a metabolite in the cascade of arachidonic acid and have various activities such as cytoprotection, oxytocic effect, algesic effect, promotion of vermicular movement of digestive tract, arousal effect, supression of gastric-acid secretion, hypotensive activity, and diuretic action.
Studies in recent years have revealed that PGE2 receptors have subtypes that play different roles from each other. Currently known subtypes are roughly classified into four groups called EP1, EP2, EP3, and EP4, respectively (Negishi M. et al, J. Lipid Mediators Cell Signaling 12, 379-391 (1995)). Examination of separate roles of these receptors with compounds that bind to specific receptors and finding compounds not to bind any other subtype receptors has made it possible to obtain drugs having less side effects.
Recently, an application disclosing that a compound having an xcfx89-chain modified with a hydroxyl group has an effect on erectile dysfunction equivalent to that of PGE1 and is less irritating has been laid open to public inspection. It also describes that the compound disclosed therein is EP2-specific (cf., WO00/02164).